1U Rackmount Server Fan Sounds (long)

A single fan designed for use in a 1U rackmount server (probably a Dell Poweredge 1950) hooked up to a benchtop power supply. Since the fan module needs to be small and move a lot of air, it's composed of two fans stuck together. It's also rather loud and powerful. In this clip, I vary the voltage supplied to the fan to gradually spin it up and down several times. When the voltage supplied to it is gradually reduced, it almost sounds like a jet engine spinning down.
The click at the beginning is the sound of me switching on the power supply. The click at the end is the sound of me switching off the power supply.

Recorded with the microphone on an iPhone.